The invention relates to a surface-mountable multilayer capacitor comprising a multilayer of metal layers which serve as electrodes and dielectric layers which are located between said metal layers, as well as two end contacts having a sprayed-metal layer which are located at two parallel side faces of the multilayer.
Surface-mountable devices (SMD's) are used in the so-called surface-mounting technique in which said electric devices are directly secured to "printed wiring" via the end contacts, this printed wiring comprising, for example, a substrate of hard paper or synthetic resin, having conductor tracks. Such a printed wiring is referred to as a printed circuit board (PCB).
A capacitor of the type mentioned in the opening paragraph is known from U.S. Pat. No. 4,531,268. In said specification, a description is given of a multilayer capacitor which is composed of a number of metallized synthetic resin foils. These synthetic resin foils form the dielectric layers and the metal layers form the electrodes. Two opposing side faces of the multilayer are provided with a porous metal layer by means of a metal-spraying process. Said sprayed-metal layers form the connections (end contacts) by means of which the capacitor is soldered to a PCB. The metallized synthetic resin foils are arranged so as to be alternately displaced relative to each other, in such a manner that successive electrodes of the multilayer are alternately connected to the one or the other end contact in an electrically conductive manner.
Applicants have found that there are a number of reasons why the above capacitor does not operate satisfactorily. Firstly, the sprayed-metal layers which serve as end contacts must be relatively thick, i.e., thicker than 150 .mu.m. This relatively large thickness is required because the sprayed-metal layers also ensure the mechanical stability of the capacitor, i.e., said sprayed-metal layers hold the individual layers of the multilayer together. As metal-spraying is a relatively expensive and inefficient process this is regarded as very disadvantageous. Secondly, it has been found that sprayed-metal end contacts exhibit mediocre soldering properties. Consequently, a soldered joint between a sprayed-metal end contact and a PCB has insufficient mechanical stability and, hence, can easily be broken. This is also undesirable. Thirdly, sprayed-metal end contacts have an irregular shape. Consequently, the dimensions of, in particular, relatively small multilayer capacitors are difficult to control. In view of the ongoing miniaturization and standardization of the dimensions of SMD components, this is experienced as a problematic to an increasing serious problem.